1. Technical Field
The present invention relates to a low-resistance and low-loss ferrite magnetic material, and a ferrite core for power transformers or accelerators.
2. Background Art
Soft magnetic ferrites are often used for cores of inductance elements of power transformers, choke coils, etc.
Ni--Cu--Zn ferrites, because of having a high specific resistance of 1.times.10.sup.8 .OMEGA..multidot.cm or more, are suitable for inductance elements for high-frequency purposes. For instance, JP-A-62-56358 discloses to apply them to low-pass filter cores, JP-A-1-101609 to apply them to inductors used at high frequencies of 1 MHz or more, and JP-A-1-101610 to apply them to chip inductors used at high frequencies of 1 MHz or more. With such ferrites, cost reductions are achievable because they can be directly wound with no provision of insulating coatings on their surfaces, as set forth in JP-A-62-56358.
However, difficulty is involved in using Ni--Cu--Zn ferrites for power transformer cores because their power loss is relatively large.
Generally, Mn--Zn ferrites are used as a core material for power transformers, and contain various subordinate components to make power loss low. However, the Mn--Zn ferrites are unsuitable for high-frequency purposes due to their specific resistance being as low as about 1.times.10.sup.3 .OMEGA..multidot.cm, and cannot be wound directly into a core as well.
Among ferrite materials known for particle accelerators there is an Ni--Cu--Zn system having such a basic composition as set forth in the aforesaid JP-A-62-56358. However, this composition system has high power loss as already mentioned, and so presents some considerable obstruction to achieving performance improvements, for instance, making the efficiency and energy of accelerators high. It has also been known so far in the art that Q characteristics are improved by the addition of CoO to Ni--Cu--Zn ferrites. Shown in FIGS. 13 and 14 are power losses and .mu.Qf products of a conventional basic composition consisting of 49 mol % of Fe.sub.2 O.sub.3, 3 mol % of CuO, 18 mol % of NiO and 30 mol % of ZnO with 0.1 to 1.0 wt % of CoO added thereto, as measured at 1 MHz-25 mT, room temperature (RT), and 100.degree. C. With 0.04 mol % of CoO added, a power loss of 240 kW/m.sup.3 is obtained at 100.degree. C. or a 27% reduction is achieved as compared with that achieved so far (330 kW/m.sup.3), with a .mu.Qf product of 9.times.10.sup.9, as can be seen from these figures. However, this value is still less than satisfactory for the aforesaid purposes, and so much more loss reductions are now desired.